Reference is made to commonly-owned application Ser. No. 013,775 filed simultaneously herewith.
The present invention is directed to a spreader roll or equivalent for a fabric such as wire or felt in a paper machine, the spreader roll being supported at the middle thereof and comprising an inner tube and an outer tube attached onto the inner tube through an intermediate part. The intermediate part thereof is substantially symmetric relative to a transverse centre plane through the roll, with the inner and outer tubes being substantially coaxial with one another when the roll is in an unbent state. Between the outer and inner tube parts, there are annular intermediate spaces at both sides of the intermediate part, the annular intermediate spaces being dimensioned to permit deflection of the inner tube and the outer tube relative to one another when the fabric passing over the roll is being tensioned. Ends or end flanges are attachable to outer ends of the inner tube, with axle journals in turn being attachable to the ends or end flanges, by means of which the roll can be journaled to rotate or revolve.
The present invention is also directed to a method for manufacturing a spreader roll in accordance with the present invention.
In a paper machine, the necessary fabrics such as wires and felts are tensioned on the rolls with the particular tension required in each situation. This tension is influenced, e.g., by the drive power transmitted by a driven roll to the fabric. By the effect of this tension, the rolls are deflected which causes detrimental effects on the conduct or running of the fabric in the machine. Firstly, the fabric tends to travel from the sides towards the centre of the machine, being wrinkled and rapidly destroyed. There is naturally an interruption caused in the paper production thereby. Another drawback is the difference in length in the fabric loop, as compared between the centre of the machine and the sides thereof, such a difference resulting from the bending of the rolls. This also results in the tendency to form wrinkles described above, as well as in detrimental wear of the fabric because of the difference in length as they glide over the rolls. In order to eliminate the problem, so-called spreader rolls or separate curved rolls (Mont Hope) have been used. The spreader rolls are made of steel, in which the spreading capacity of one roll is small due to the well-known high elastic modulus thereof; therefore, several such rolls are required in some applications.
The prior-art spreader rolls supported at the middle thereof comprise an inner tube made of steel and having a circular cylindrical shape, in addition to an outer tube made of steel attached onto the inner tube, e.g., by means of shrink-on joints. The tubes are joined symmetrically together relative to the centre plane of the roll. At the ends of the inner tube, there are end flanges and axle journals attached to the end flanges. Between the inner mantle and the outer mantle of the roll, in the middle region thereof, a shrink-on joint is used. The formation of this joint and of corresponding other shrink-on joints has proven to be difficult and expensive.
Moreover, a drawback of the shrink-on joints is that the inner tube tends to become broken at the lateral area of the joint. This is caused largely by vibration wear and fatique fracturing, which start from the lateral areas of the shrink-on joints. The formation of the shrink-on joint is expensive especially because the inner face of the outer tube of the roll, which is not easily accessible, must be machined to quite precise dimensions.
The prior-art metallic spreader rolls described above also have the drawback that the rolls become quite heavy, which causes, e.g., detrimental deflection, with the spreading effect not being as good as desirable. The cantilevering of the heavy rolls is often problematic when the rolls are installed in older paper machines in connection with the renewal thereof.
The length of a typical prior-art spreader roll made of steel by means of shrink-on joints is L=9,450 mm, with an outer diameter Du=1010 mm., in which case the weight of the double mantle of the roll becomes even as high as about 13,000 kg.
With respect to the prior art related to the present invention, it has been further ascertained that, e.g., paper machine rolls made of plastic reinforced with fibre glass are known in the prior art, e.g., as wire guide rolls, However, the fiber glass coating is used exclusively for protection against corrosion, and not as a structural component of the roll.